In recent years, thermal transfer systems have been developed to obtain prints from pictures which have been generated electronically, e.g. from a color video camera. According to one way of obtaining such prints, an electronic picture is first subjected to color separation by color filters. The respective color-separated images are then converted into electrical signals. These signals are then operated on to produce cyan, magenta and yellow electrical signals. These signals are then transmitted to a thermal printer. To obtain the print, a cyan, magenta or yellow dye-donor element is placed face-to-face with a dye-receiving element. The two are then inserted between a thermal printing head and a platen roller. A line-type thermal printing head is used to apply heat from the back of the dye-donor sheet. The thermal printing head has many heating elements and is heated up sequentially in response to the cyan, magenta, black and yellow signals. The process is then repeated for the other two colors. A color hard copy is thus obtained which corresponds to the original picture viewed on a screen. Further details of this process and an apparatus for carrying it out are contained in U.S. Pat. No. 4,621,271 by Brownstein entitled "Apparatus And Method For Controlling A Thermal Printer Apparatus," issued Nov. 4, 1986, the disclosure of which is hereby incorporated by reference.
Another way to thermally obtain a print using the electronic signals described above is to use a laser instead of a thermal printing head. In such a system, the donor sheet includes a material which strongly absorbs at the wavelength of the laser. When the donor is irradiated, this absorbing material converts light energy to thermal energy and transfers the heat to the dye in the immediate vicinity, thereby heating the dye to its vaporization temperature for transfer to the receiver. The absorbing material may be present in a layer beneath the dye and/or it may be admixed with the dye. The laser beam is modulated by electronic signals which are representative of the shape and color of the original image, so that each dye is heated to cause volatilization only in those areas in which its presence is required on the receiver to reconstruct the color of the original object. Further details of this process are found in GB No. 2,083,726A, the disclosure of which is hereby incorporated by reference.
Conventionally, there are known a thermosensitive image transfer sheet comprising a support material and a sublimable dye layer formed on the support material, and a thermosensitive image transfer sheet comprising a support material and a thermofusible ink layer comprising a thermofusible material and a pigment, capable of forming images on a receiving sheet by subjecting the thermosensitive image transfer medium to thermal printing.
The method which uses a sublimable dye is superior in image gradation reproduction, but is low in thermal sensitivity and has the drawback of inferior durability of the image. On the other hand, the method which uses a thermofusible material and a pigment is superior in thermosensitivity and the durability of the produced images, but has the drawback of providing poor image gradation.
At the present time, color proofing requires the use of silver halide color separation films which represent all four colors in an image. The intention of digital color proofing is to construct a color proof from digital data without making the silver halide separation films. One approach to creating a digital image is to use a laser scanner to scan a laser beam over a photosensitive material, modulating the laser beam with digital image data. Photosensitive color films which use diazo technology are not very sensitive to laser light.
Thermal wax transfer is a process whereby a wax image which absorbs actinic light is thermally transferred to a carrier sheet upon which is coated a colored photosensitive layer. The present invention combines the digital imaging speed of thermal wax transfer with the color/density control of pre-coated photosensitive color films.